The Conspiracy of Catiline (Sallust's first published work) contains the history of the memorable year 63. Sallust adopts the usually accepted view of Catiline, and describes him as the deliberate foe of law, order and morality, and does not give a comprehensive explanation of his views and intentions. (Note that Catiline had supported the party of Sulla, which Sallust had opposed.) Mommsen's suggestion — that Sallust particularly wished to clear his patron (Caesar) of all complicity in the conspiracy — may have contained some truth.
In writing about the conspiracy of Catiline, Sallust's tone, style, and descriptions of aristocratic behavior show him as deeply troubled by the moral decline of Rome. While he inveighs against Catiline's depraved character and vicious actions, he does not fail to state that the man had many noble traits — indeed all that a Roman man needed to succeed. In particular, Sallust shows Catiline as deeply courageous in his final battle.
This subject gave Sallust the opportunity of showing off his rhetoric at the expense of the old Roman aristocracy, whose degeneracy he delighted to paint in the blackest colours. On the whole, he does not treat Cicero unfairly.